In recent years, as a technique enabling optical processing in a region that is smaller than a wavelength of a light (visible light: 0.4 microns to 0.8 microns), attention has been focused on a technique of utilizing a near-field light (light arriving at only a region with a distance shorter than a wavelength of light). For example, in the field of a scanning near-field optical microscope, an optical probe having a fine aperture that is smaller than a wavelength of light at a distal end of the probe, as described in Patent Document 1, is used as an optical waveguide. In addition, at the time of observing a small region of a sample surface, a fine aperture of the optical probe is disposed in proximity to the small region targeted for observation so as to bring an optical field (near-field) that seeps out in the vicinity of the surface of the fine aperture into contact with the sample surface.
Then, only the small region of the sample surface coupled with this near field is irradiated with the light (near-field light), and then, reflected light, scattering light, or transmitted light from the sample due to that irradiation is detected, thereby locally observing and evaluating the small region. Therefore, with respect to such an optical probe that is a type of optical waveguide, a variety of optical probes have been conventionally proposed as optical waveguides in order to contribute to a request for downsizing a recording bit in an optical recording medium such as CDs, for example, or evaluation or the like of a semiconductor manufacturing process for carrying out a fine processing on the order of sub-microns.
Incidentally, like the optical probe described in Patent Document 1, an optical probe which forms a fine aperture at the distal end of the probe, irradiates a sample surface through the fine aperture, and detects a reflected light or the like through the fine aperture is referred to as an aperture probe. On the other hand, an optical probe which forms a distal end of the probe as a sharp end having a significantly small radius of curvature like a metal needle and detects scattering light by means of another detection optical probe produced at the time of inserting the end of the probe into a near-field optical region generated by irradiating the sample surface under a full reflection condition is referred to as an apertureless probe.
In the meantime, the fine aperture of an aperture probe is smaller than a wavelength of light, and thus, the light intensity of the near-field light is unavoidably very weak. For example, in the case of an illumination mode in which irradiation of the near-field light and a focusing of the light obtained from a sample are carried out through the same aperture, the light intensity of the near-field light that seeps out from the fine aperture of the aperture probe becomes very weak, i.e., on the order of about 1/1000 of the light intensity of the light introduced into the aperture probe. Therefore, for example, at the time of high speed writing or readout in an optical information recording apparatus or the like, a problem such as an insufficient amount of light may occur. Thus, at the time of practically using the aperture probe, there is a need for increasing the light intensity of the near-field light that seeps out from the fine aperture.
However, if a light source is strengthened in order to increase the light intensity of the near-field light, cost is increased. On the other hand, if the distal end aperture is increased, the spread of the light that seeps out from this aperture increases, resulting in the lowered resolution. Namely, in any case, a problem with use of the aperture probe cannot be properly avoided. On the other hand, the resolution (resolving power) of an apertureless probe can be improved more remarkably than that of an aperture probe. However, if the distal end of the apertureless probe is actually inserted into the near-field optical region, the scattering light occurs not only at the distal end of the probe, but also at a portion other than the distal end of the probe. Therefore, an S/N ratio (Signal/Noise Ratio) of the apertureless probe is worsened than that of the aperture probe, and the detection sensitivity may be lowered. Further, when using the apertureless probe, and a detection optical probe must be further provided, resulting in high cost.
[Patent Document 1] Japanese Laid-Open Patent Publication No. 2002-221478